A treatment system and method for recovering ammonium sulfate from rare earth wastewater by membrane process

Abstract

The application discloses a treatment system and method for recovering ammonium sulfate in rare earth wastewater by a membrane method, and the system comprises a filtering device, a nanofiltration membrane filtering and separating device and a reverse osmosis membrane filtering and separating device. The application provides the treatment system and method for recovering ammonium sulfate in rare earth wastewater and rare earth wastewater by the membrane method in view of defects of an existing rare earth wastewater treatment process, and the treatment system and method have the advantages of a short process flow, a small land occupation, a small investment, effective recovery and utilization of ammonium sulfate in wastewater, high water quality of treated effluent, low operation cost, strong adaptability to wastewater quality and good continuous effect.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling and environmental protection, and specifically relates to a membrane-based treatment system and method for recovering ammonium sulfate from rare earth wastewater. Background Technology

[0002] Rare earth elements are a collective term for the lanthanides and scandium / yttrium, totaling seventeen metallic elements in the periodic table. They are valuable strategic resources, and there are 250 types of rare earth minerals in nature. my country is a major producer of rare earth resources and products. Rare earth mining is carried out according to different mineral types, with typical examples being the Baotou cerium fluorocarbonate deposit and ion-adsorption rare earth deposits in the south. Ion-adsorption rare earth minerals are products of granite weathering, existing in ionic form in soil layers. The mining method involves soaking the soil in ammonium sulfate solution to displace the ionic rare earth elements into the solution. This mining method includes three specific implementations: heap leaching, pond leaching, and in-situ leaching. The first two are now prohibited, while in-situ leaching has been widely adopted. In-situ leaching involves directly drilling tunnels in the mine, injecting ammonium sulfate solution, collecting the mother liquor below, and then precipitating it with ammonium bicarbonate to obtain rare earth carbonates. In-situ leaching is the primary mining method for ion-adsorption rare earth minerals. However, after mining, a large amount of wastewater containing ammonium sulfate continuously flows out year after year, day after day. The concentration of ammonium sulfate in this wastewater ranges from approximately 150 to 5000 mg / L, and the water is mostly acidic, with a pH between 2 and 6.5. Direct discharge of this wastewater into surrounding natural water bodies can lead to severe exceedances of ammonia nitrogen levels in the local aquatic environment. Therefore, it is essential to treat rare earth ammonium-containing wastewater. Currently, there are many methods for treating rare earth ammonium-containing wastewater, but successful cases are few. These methods mainly include physical, chemical, and biological methods. Physical methods include reverse osmosis, distillation, and soil irrigation; chemical methods include ion exchange, ammonia stripping, breakpoint chlorination, incineration, chemical precipitation, electrodialysis, and electrochemical treatment; and biological methods include algae cultivation, biological nitrification, and immobilized biological technologies. Biological removal of rare earth wastewater containing ammonium sulfate refers to the process by which ammonia nitrogen in the wastewater undergoes a series of reactions, such as nitrification and denitrification, under the action of various microorganisms, ultimately forming nitrogen gas, thereby achieving the purpose of removing ammonia nitrogen.

[0003] The ammonia stripping method involves adjusting the pH of rare earth wastewater from 2-6.5 to 8.5-9.5, adding a coagulant for coagulation and sedimentation to remove impurities such as silicates, aluminates, and iron. Then, sodium hydroxide solution is added to adjust the pH to 11.5-12, allowing ammonium ions in ammonium sulfate to reach equilibrium with ammonia molecules. The wastewater then enters an ammonia evaporator for evaporation. The ammonia evaporates into ammonia gas, which is then cooled and absorbed in an absorption tower. In the absorption tower, sulfuric acid or hydrochloric acid reacts to produce ammonium sulfate or ammonium chloride, which is then evaporated and crystallized to remove ammonium sulfate from the rare earth wastewater. This method requires significant investment and has high operating costs. Furthermore, to prevent scaling in the evaporator, coagulation and sedimentation are necessary, generating a large amount of sludge. Additionally, the ammonia stripping method consumes a lot of energy and reagents, the evaporator is highly susceptible to corrosion, and the evaporation equipment has a short lifespan. Furthermore, since most rare earth wastewater has a pH of 2.5–4, it is highly acidic. Due to the presence of silicates and aluminates, a strong buffering system is formed. Adjusting the pH from 2.5–4 to 8.5–9.5 requires a large amount of sodium hydroxide solution, resulting in high operating costs. Therefore, the ammonia stripping method is not economically viable.

[0004] There are many biological nitrogen removal processes, but their mechanisms are basically the same, all requiring nitrification and denitrification stages. Nitrification, under aerobic conditions, involves aerobic nitrifying bacteria oxidizing ammonia nitrogen in wastewater to nitrite or nitrate. It includes two basic reaction steps: the conversion of ammonia nitrogen to nitrite by nitrite-oxidizing bacteria, and the conversion of nitrite to nitrate by nitrifying bacteria. Both nitrite-oxidizing and nitrifying bacteria are autotrophic, utilizing carbon sources in the wastewater and obtaining energy through redox reactions with NH3-N. The reaction equations are as follows:

[0005] Nitrification: 2NH4++3O2→2NO2-+2H2O+4H+

[0006] Nitrification: 2NO2- + O2 → 2NO3-

[0007] The suitable pH value for nitrifying bacteria is 8.0–8.4, and the optimal temperature is 35℃. Temperature has a significant impact on nitrifying bacteria; the nitrification reaction almost stops when the temperature drops to 10℃. DO concentration: 2–3 mg / L; BOD5 loading: 0.06–0.1 kg BOD5 / (kg MLSS·d); sludge age: 3–5 days or more. Under anoxic conditions, denitrifying bacteria (denitrifying bacteria) reduce nitrite and nitrate to nitrogen gas, which escapes from the wastewater. The process of reducing nitrate or nitrite produced during nitrification to N2 due to the action of facultative denitrifying bacteria (denitrifying bacteria) is called denitrification. The electron donor in the denitrification process is various organic substrates (carbon sources). Taking methanol as an example, the reaction formula is:

[0008] 6NO3-+2CH3OH→6NO2-+2CO2+4H2O

[0009] 6NO2-+3CH3OH→3N2+3CO2+3H2O+6OH-

[0010] The suitable pH value for denitrifying bacteria is 6.5 to 8.0; the optimal temperature is 30℃. When the temperature is below 10℃, the denitrification rate decreases significantly, and when the temperature drops to 3℃, denitrification will stop.

[0011] However, biological nitrification and denitrification methods, besides being primarily suitable for water bodies with relatively low ammonia nitrogen concentrations and appropriate carbon-to-nitrogen ratios, also require the consumption of large amounts of carbon sources during the nitrification and denitrification processes. Since high-ammonia wastewater generated during rare earth mining and processing contains almost no carbon source, all carbon sources must be externally added if biological methods are used. Furthermore, the ammonium ion concentration in high-ammonia wastewater from rare earth mining and processing is as high as 150–5000 mg / L. Therefore, in addition to requiring large-scale biological treatment tanks, a large amount of carbon source needs to be added during operation, making production costs unacceptable. Moreover, rare earth wastewater contains a large amount of ammonium sulfate; direct treatment not only wastes ammonium sulfate resources but also leads to high treatment costs. Ammonia stripping is not only costly to operate but also causes severe scaling and equipment corrosion in the evaporator. Therefore, there is an urgent need for a rare earth wastewater treatment system that can recover ammonium sulfate from rare earth wastewater, has high treatment efficiency, and low investment and operating costs. Summary of the Invention

[0012] In order to solve the above-mentioned technical problems, the purpose of this invention is to provide a treatment system and method for recovering ammonium sulfate from rare earth wastewater using a membrane method.

[0013] This invention is achieved through the following technical solution:

[0014] A membrane-based system for recovering ammonium sulfate from rare earth wastewater includes a filtration device, a nanofiltration membrane filtration separation device, and a reverse osmosis membrane filtration separation device.

[0015] The filtration device includes a rare earth wastewater regulating tank, a first high-pressure pump, a filter, a first eluent storage tank, a first backwash water tank, and a filtrate storage tank. The inlet of the first high-pressure pump is connected to the rare earth wastewater regulating tank, the outlet of the first high-pressure pump is connected to the inlet of the filter, the outlet of the filter is connected to the inlet of the filtrate storage tank, the backwash water outlet of the filter is connected to the first eluent storage tank, and the outlet of the first backwash water tank is connected to the filter.

[0016] The nanofiltration membrane filtration separation device includes a second high-pressure pump, a nanofiltration membrane module, a nanofiltration eluent storage tank, a first chemical washing tank, a second backwash water tank, a first dialysis fluid storage tank, a nanofiltration membrane concentrate storage tank, and a sludge thickening tank. The inlet of the second high-pressure pump is connected to the filtrate storage tank, and the outlet of the second high-pressure pump is connected to the inlet of the nanofiltration membrane module. The dialysis fluid outlet of the nanofiltration membrane module is connected to the inlet of the first dialysis fluid storage tank, and the concentrate outlet of the nanofiltration membrane module is connected to the nanofiltration membrane concentrate storage tank. The outlet of the first dialysis fluid storage tank is connected to the reverse osmosis membrane filtration separation device, the eluent outlet of the nanofiltration membrane module is connected to the nanofiltration eluent storage tank, the supernatant outlet of the nanofiltration eluent storage tank is connected to a rare earth wastewater equalization tank, and the sludge outlet of the nanofiltration eluent storage tank is connected to the sludge thickening tank.

[0017] The reverse osmosis membrane filtration separation device includes a third high-pressure pump, a reverse osmosis membrane module, a reverse osmosis eluent storage tank, a second chemical washing tank, a second backwash water tank, and a second dialysis fluid storage tank. The inlet of the third high-pressure pump is connected to the first dialysis fluid storage tank, the outlet of the third high-pressure pump is connected to the inlet of the reverse osmosis membrane module, the dialysis fluid outlet of the reverse osmosis membrane module is connected to the inlet of the second dialysis fluid storage tank, and the concentrate outlet of the reverse osmosis membrane module is connected to the nanofiltration membrane concentrate storage tank.

[0018] In this embodiment of the invention, the filter is a mechanical filter or a membrane module.

[0019] In this embodiment of the invention, the mechanical filter is one of sand filter, activated sand filter, multi-media filter, V-type filter, fine filter, or fiber filter cartridge filter.

[0020] In this embodiment of the invention, the membrane module is a type of microfiltration or ultrafiltration membrane module.

[0021] In this embodiment of the invention, the microfiltration or ultrafiltration membrane module is one of a tubular membrane module, a spiral wound membrane module, a hollow fiber membrane module, or a flat sheet membrane module.

[0022] In this embodiment of the invention, the filtration device further includes a booster pump and a security filter. The inlet of the booster pump is connected to the rare earth wastewater regulating tank, the outlet of the booster pump is connected to the inlet of the security filter, and the outlet of the security filter is connected to the membrane module.

[0023] In this embodiment of the invention, the nanofiltration membrane module of the nanofiltration separation device is a nanofiltration membrane module with a magnesium sulfate retention of greater than or equal to 98%. The membrane material of the nanofiltration membrane module is an organic membrane and a composite membrane. The working pressure is: 15-55 bar at the inlet and 13.5-53 bar at the outlet. The pressure difference between the inlet and outlet is 1.5-2.0 bar.

[0024] In this embodiment of the invention, the reverse osmosis membrane module of the reverse osmosis membrane filtration separation device is a reverse osmosis filter membrane module with a sodium chloride rejection of greater than or equal to 98%, the membrane material of the reverse osmosis membrane module is an organic membrane or a composite membrane, and the working pressure is 15-75 bar at the inlet and 13.5-73 bar at the outlet.

[0025] In this embodiment of the invention, the nanofiltration membrane module or reverse osmosis membrane module is one of a tubular membrane module, a spiral wound membrane module, a hollow fiber membrane module, a flat sheet membrane module, or a disc tube membrane module (DTNF or DTRO).

[0026] A membrane method for recovering ammonium sulfate from rare earth wastewater comprises the following steps:

[0027] (1) Rare earth wastewater filtration: The rare earth wastewater to be treated is collected in the rare earth wastewater equalization tank, and then filtered by a lift pump to obtain filtrate and filter residue. The filtrate is stored in the filtrate storage tank.

[0028] (2) Nanofiltration membrane filtration separation, concentration and recovery of ammonium sulfate solution: The filtrate obtained from the filtration in step (1) and stored in the filtrate storage tank is sent to the nanofiltration membrane filtration separation device by a high-pressure pump. The inlet pressure is 15-55 bar and the outlet pressure is 13.5-53 bar.

[0029] Rare earth wastewater is separated into a concentrated solution containing 2-6% ammonium sulfate and a dialysis solution with an ammonium sulfate concentration of less than 700 mg / L by nanofiltration. These solutions are stored separately in a nanofiltration membrane concentrated solution storage tank and a first dialysis solution storage tank. The yield of the concentrated solution containing 2-6% ammonium sulfate is 15-20%, and the yield of the dialysis solution with an ammonium sulfate concentration of less than 700 mg / L is 80-85%. The concentrated solution containing 2-6% ammonium sulfate is the recovered ammonium sulfate solution and can be used as a leaching solution for rare earth mining.

[0030] (3) Reverse osmosis membrane filtration: The nanofiltration solution obtained in step (2) and stored in the first dialysis solution storage tank is pumped into the reverse osmosis membrane filtration separation device using a third high-pressure pump. The working inlet pressure is 15-75 bar, the outlet pressure is 13.5-73 bar, and the pressure difference is 1-1.5 bar. The reverse osmosis membrane filtration separation device separates the nanofiltration solution of rare earth wastewater into a concentrated solution containing ammonium sulfate with a concentration of 3500-4500 mg / L and a solution containing ammonia nitrogen with a concentration of less than 25 mg / L. The solutions are stored separately in a nanofiltration membrane concentrate tank and a second dialysis solution tank. The yield of the concentrate containing ammonium sulfate concentration of 3500-4500 mg / L is 5-15%. The yield of the dialysis solution containing ammonia nitrogen concentration of less than 25 mg / L is 85-95%. The concentrate containing ammonium sulfate concentration of 3500-4500 mg / L is pumped back to the nanofiltration membrane filtration separation device for further nanofiltration. The reverse osmosis dialysis solution containing ammonia nitrogen concentration of less than 25 mg / L is discharged into natural water bodies after metering.

[0031] The membrane-based treatment system for recovering ammonium sulfate from rare earth wastewater according to the present invention has the following beneficial effects:

[0032] 1. The treatment of rare earth wastewater only includes three main processes: filtration, nanofiltration and reverse osmosis filtration. This allows for the full recovery and utilization of ammonium sulfate resources in rare earth wastewater, and the production process is simpler and the operation is easier.

[0033] 2. This invention can recover 80-95% of ammonium sulfate from rare earth wastewater, resulting in better water quality. The recovered ammonium sulfate solution can be purified and used as a mining agent for rare earths, saving ammonium sulfate resources, reducing resource waste, and mitigating the environmental pollution caused by rare earth development.

[0034] 3. The operating cost of using the system provided by this invention to treat rare earth wastewater is less than 15 yuan / ton, the water retention time is only 1.0 to 2.0 hours, the circulation is faster and the efficiency is higher, and the overall device occupies less than one-tenth of the area of ​​existing traditional devices, which is small in size.

[0035] 4. No sludge is produced. Attached Figure Description

[0036] To more clearly illustrate the technical solution of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a process block diagram of a membrane-based treatment system for recovering ammonium sulfate from rare earth wastewater according to the present invention.

[0038] Figure 2 This is a process flow diagram of a membrane-based treatment system for recovering ammonium sulfate from rare earth wastewater according to the present invention.

[0039] Figure 3 This is a process block diagram of another membrane-based treatment system for recovering ammonium sulfate from rare earth wastewater according to the present invention.

[0040] Figure 4 This is a process flow diagram of another membrane-based treatment system for recovering ammonium sulfate from rare earth wastewater according to the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0042] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. In the description of the invention, it should be understood that the terms "upper," "lower," "top," "bottom," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein.

[0043] The present invention provides a membrane-based treatment system for recovering ammonium sulfate from rare earth wastewater, comprising: a filtration device 100, a nanofiltration membrane filtration separation device 200, and a reverse osmosis membrane filtration separation device 300.

[0044] The filtration device 100 includes: a rare earth wastewater equalization tank 110, a first high-pressure pump 120, a filter 130, an eluent storage tank 140, a first backwash water tank 150, and a filtrate storage tank 160. The filtration device 100 is used to filter and remove solid particulate impurities from the rare earth wastewater to prevent subsequent membrane clogging. The inlet of the first high-pressure pump 120 is connected to the rare earth wastewater equalization tank 110, the outlet of the first high-pressure pump 120 is connected to the inlet of the filter 130, the outlet of the filter 130 is connected to the inlet of the filtrate storage tank 160, the backwash water outlet of the filter 130 is connected to the eluent storage tank 140, and the outlet of the first backwash water tank 150 is connected to the filter.

[0045] The filter 130 is either a mechanical filter or a membrane module. When the filter is a mechanical filter, refer to the attached instruction manual. Figure 1 and appendix Figure 2The mechanical filter 130 can be one of the following: sand filter, activated sand filter, multi-media filter, V-type filter, fine filter, or fiber filter cartridge filter.

[0046] When the filter is a membrane module 160', it is a type of microfiltration or ultrafiltration membrane module. (See attached instruction manual.) Figure 3 and appendix Figure 4 The filtration device 100 includes a rare earth wastewater equalization tank 110', a booster pump 120', a security filter 130', an intermediate filtrate storage tank 140', a first high-pressure pump 150', a membrane module 160', an eluent storage tank 170', a backwash water tank 180', and a filtrate storage tank 190'. The inlet of the booster pump 120' is connected to the wastewater collection tank 110', and the outlet of the booster pump 120' is connected to the inlet of the security filter 130'. After preliminary filtration by the security filter, the preliminary filtrate in the intermediate filtrate storage tank 140' is then passed into the membrane module 160' for further filtration. Alternatively, the security filter step can be omitted, and the wastewater equalization tank 110' can be directly connected to the membrane module 160' via the first high-pressure pump. The backwash liquid outlet of membrane module 160' is connected to the eluent storage tank 170', the outlet of the backwash clear water tank 180' is connected to the membrane module, and the outlet of the membrane module is connected to the filtrate storage tank 190'. The microfiltration or ultrafiltration membrane module is one of a tubular membrane module, a spiral wound membrane module, a hollow fiber membrane module, or a flat sheet membrane module, wherein the tubular membrane module is one of an organic tubular membrane module or a ceramic membrane module.

[0047] The nanofiltration membrane filtration separation device 200 is used to filter and separate ammonium sulfate from rare earth wastewater, concentrating the ammonium sulfate-containing rare earth wastewater into an ammonium sulfate solution with utilization value. See also... Figure 1-2 Alternatively, as described in sections 3-4, the nanofiltration membrane filtration separation device 200 includes a second high-pressure pump 210, a nanofiltration membrane module 220, a nanofiltration eluent storage tank 230, a first chemical washing tank 240, a second backwash water tank 250, a first dialysate storage tank 260, a nanofiltration membrane concentrate storage tank 270, and a sludge thickening tank 280. The second high-pressure pump 210 is used to transport the filtrate from the filtrate storage tanks 160 / 190' to the nanofiltration membrane module 220. The nanofiltration membrane module 220 is used to separate wastewater into a concentrated solution with a higher ammonium sulfate concentration and a dialysate containing a small amount of ammonium sulfate. The nanofiltration membrane concentrate (ammonium sulfate concentrate) storage tank 270 is used to store the high-concentration ammonium sulfate concentrate separated by the nanofiltration membrane module 220. The first dialysate storage tank 260 is used to store the dialysate containing a small amount of ammonium sulfate separated by the nanofiltration membrane module 220.

[0048] Structurally, the outlet of the high-pressure pump 210 is connected to the inlet of the nanofiltration membrane module 220, the dialysis fluid outlet of the nanofiltration membrane module 220 is connected to the inlet of the first dialysis fluid storage tank 260, the concentrate outlet of the nanofiltration membrane module 220 is connected to the nanofiltration membrane concentrate (ammonium sulfate concentrate) storage tank 270, and the outlet of the first dialysis fluid storage tank 260 is connected to the inlet of the reverse osmosis membrane module 320 of the reverse osmosis filtration device 300 via the third high-pressure pump 310. The outlets of the second backwash water tank 250 and the first chemical washing tank 240 are connected to the nanofiltration membrane module 220. The eluent outlet of the nanofiltration membrane module 220 is connected to the nanofiltration eluent storage tank 230. The supernatant outlet of the nanofiltration eluent storage tank 230 is connected to the rare earth wastewater equalization tank 110 / 110'. The sludge outlet of the nanofiltration eluent storage tank 230 is connected to the sludge thickening tank 280.

[0049] The reverse osmosis membrane filtration separation device 300 is used to filter and separate the dialysate after nanofiltration, separating and concentrating the nanofiltration dialysate containing ammonium sulfate into a reverse osmosis concentrate with a higher ammonium sulfate content and a dialysate that meets emission standards. The reverse osmosis membrane filtration separation device 300 includes a third high-pressure pump 310, a reverse osmosis membrane module 320, a reverse osmosis eluent storage tank 330, a second chemical washing tank 340, a second backwash water tank 350, and a second dialysate storage tank 360. The third high-pressure pump 310 is used to input the nanofiltration dialysis solution of rare earth wastewater into the reverse osmosis membrane module 320 for filtration. The reverse osmosis membrane module 320 is used to further filter the nanofiltration dialysis solution of rare earth wastewater, separating it into a concentrated solution with a higher concentration of ammonium sulfate and a dialysis solution with an ammonium sulfate concentration of less than 95 mg / L (ammonia nitrogen concentration ≤25 mg / L). The membrane concentrate (ammonium sulfate concentrate) storage tank 270 is used to pump back the high-concentration ammonium sulfate concentrate separated by the nanofiltration device 200. The second dialysis solution storage tank 360 is used to store the dialysis solution containing a small amount of ammonium sulfate separated by the reverse osmosis membrane module 320. The inlet of the third high-pressure pump 310 is connected to the first dialysis fluid storage tank 260, and the outlet of the third high-pressure pump 310 is connected to the inlet of the reverse osmosis membrane module 320. The dialysis fluid outlet of the reverse osmosis membrane module 320 is connected to the inlet of the second dialysis fluid storage tank 360, and the concentrate outlet of the reverse osmosis membrane module 320 is connected to the membrane concentrate (ammonium sulfate concentrate) storage tank 270. The outlets of the third backwash water tank 350 and the second chemical washing tank 340 are connected to the reverse osmosis membrane module 320, the eluent outlet of the reverse osmosis membrane module 320 is connected to the reverse osmosis eluent storage tank 330, and the sludge outlet of the reverse osmosis eluent storage tank 330 is connected to the sludge thickening tank 280.

[0050] The present invention provides a membrane-based method for recovering ammonium sulfate and treating rare earth wastewater, specifically comprising three steps: filtration, nanofiltration membrane filtration, and reverse osmosis membrane filtration.

[0051] (1) Rare earth wastewater filtration: The rare earth wastewater to be treated is collected in the rare earth wastewater equalization tank, and then filtered by a lift pump to obtain filtrate and filter residue. The filtrate is stored in the filtrate storage tank.

[0052] (2) Nanofiltration membrane filtration separation, concentration and recovery of ammonium sulfate solution: The filtrate obtained from the filtration in step (1) and stored in the filtrate storage tank is sent to the nanofiltration membrane filtration separation device by a high-pressure pump. The inlet pressure is 15-55 bar and the outlet pressure is 13.5-53 bar.

[0053] Rare earth wastewater is separated into a concentrated solution containing 2-6% ammonium sulfate and a dialysis solution with an ammonium sulfate concentration of less than 700 mg / L by nanofiltration. These solutions are stored separately in a nanofiltration membrane concentrated solution storage tank and a first dialysis solution storage tank. The yield of the concentrated solution containing 2-6% ammonium sulfate is 15-20%, and the yield of the dialysis solution with an ammonium sulfate concentration of less than 700 mg / L is 80-85%. The concentrated solution containing 2-6% ammonium sulfate is the recovered ammonium sulfate solution and can be used as a leaching solution for rare earth mining.

[0054] (3) Reverse osmosis membrane filtration: The nanofiltration solution obtained in step (2) and stored in the first dialysis solution storage tank is pumped into the reverse osmosis membrane filtration separation device using a third high-pressure pump. The working inlet pressure is 15-75 bar, the outlet pressure is 13.5-73 bar, and the pressure difference is 1-1.5 bar. The reverse osmosis membrane filtration separation device separates the nanofiltration solution of rare earth wastewater into a concentrated solution containing ammonium sulfate with a concentration of 3500-4500 mg / L and a solution containing ammonia nitrogen with a concentration of less than 25 mg / L. The solutions are stored separately in a nanofiltration membrane concentrate tank and a second dialysis solution tank. The yield of the concentrate containing ammonium sulfate concentration of 3500-4500 mg / L is 5-15%. The yield of the dialysis solution containing ammonia nitrogen concentration of less than 25 mg / L is 85-95%. The concentrate containing ammonium sulfate concentration of 3500-4500 mg / L is pumped back to the nanofiltration membrane filtration separation device for further nanofiltration. The reverse osmosis dialysis solution containing ammonia nitrogen concentration of less than 25 mg / L is discharged into natural water bodies after metering.

[0055] After treatment by the membrane-based rare earth wastewater treatment system of the present invention, 95-98% of the ammonium sulfate in the rare earth wastewater is recovered and reused. The effects of each step in the wastewater treatment process on ammonium sulfate removal are shown in Table 1.

[0056] Table 1. Effect of each step in the removal of ammonium sulfate from rare earth wastewater.

[0057] Processing device filter Nanofiltration membrane filtration Reverse osmosis membrane filtration Particulate solids ≤ 10mg / L 1mg / L 0.5 mg / L Ammonium sulfate concentration of concentrated solution ≤ No concentrate 6000~16000mg / L 1500~4500mg / L Ammonia nitrogen concentration in membrane dialysis solution ≤ 700mg / L 25mg / L

[0058] The effluent from the rare earth wastewater to be treated, after being treated through three steps of filtration, nanofiltration, and reverse osmosis, has the following effluent parameters: ammonia nitrogen ≤ 1.5 mg / L, total nitrogen ≤ 1.5 mg / L, total phosphorus ≤ 0.1 mg / L, and other parameters meet the emission standards in Table 2 of the "Rare Earth Industry Pollutant Emission Standard" (GB26451-2011).

[0059] The present invention will be described in detail below with reference to the embodiments.

[0060] Example 1

[0061] See Figure 1 and Figure 2 This embodiment provides a membrane-based system for recovering ammonium sulfate and rare earth wastewater from rare earth wastewater. The system includes a filtration device, a disc tube nanofiltration membrane separation device, and a disc tube reverse osmosis membrane separation device. The filter is a V-type filter. The outlet of the second dialysis fluid storage tank 360 is connected to the metering tank of the rare earth wastewater treatment system, and the water is metered and discharged into a natural water body.

[0062] In this embodiment, the influent indicators and effluent compliance indicators of the rare earth wastewater to be treated are shown in Table 2.

[0063] Table 2

[0064] Serial Number project Influent water parameters (mg / L) Effluent effluent standards (mg / L) Removal rate (%) 1 COD 25 20 20.00 2 BOD 10 6 40.00 3 SS 200 5 97.50 4 Total nitrogen (as N) 1630 1.5 99.91 5 Ammonia nitrogen (as N) 1615 1.0 99.94 6 Total phosphorus (as P) 0.5 0.1 80.00 7 Color intensity (dilution factor) 10 2 80 8 pH 3.5 6～9 -

[0065] This embodiment employs a method for recovering ammonium sulfate and treating rare earth wastewater from rare earth wastewater, which sequentially includes three steps: V-type filter bed filtration, disc tube nanofiltration membrane filtration, and disc tube nanofiltration membrane filtration. Specifically:

[0066] The rare earth wastewater to be treated is collected in the rare earth wastewater equalization tank 110. The rare earth wastewater is pumped into the filter 130 by the first high-pressure pump 120 to obtain filtrate, which is then stored in the filtrate storage tank 160. Solid particles are removed and the solids are collected in the filter residue collection tank.

[0067] The filtrate obtained from filtration and stored in filtrate storage tank 160 is pumped by a second high-pressure pump 210 into a disc tube nanofiltration membrane filtration separation and concentration device 200, which has a magnesium sulfate rejection rate of 98%. The inlet water pressure of the nanofiltration membrane module is adjusted to 25 bar at the inlet and 23.5 bar at the outlet. The nanofiltration membrane module 220 separates the nanofiltration concentrate and nanofiltration dialysate. The nanofiltration concentrate effluent is stored in nanofiltration concentrate storage tank 270, and the nanofiltration dialysate effluent is stored in the first dialysate storage tank 260. The water production rate of the nanofiltration membrane concentrate is measured to be 12%, and the ammonia nitrogen concentration of ammonium sulfate increases from 1630 mg / L to 11750 mg / L, which is equivalent to an ammonium sulfate concentration of 4.519%. The water production rate of the nanofiltration dialysate is 88%, and its ammonium sulfate concentration is measured to be 253 mg / L. The concentrated solution containing 11750 mg / L of ammonium sulfate is the recovered ammonium sulfate solution, which is then used for rare earth leaching.

[0068] The nanofiltration membrane dialysis solution is pumped into the reverse osmosis membrane module 320 of the reverse osmosis membrane filtration device 300 by the third high-pressure pump 310. After filtration and separation by the reverse osmosis membrane module 320, it is separated into concentrate and dialysis solution. The reverse osmosis membrane concentrate (ammonium sulfate concentrate) enters the concentrate storage tank 270, and the reverse osmosis membrane dialysis solution enters the second dialysis solution storage tank 360. The pollutant indicators of the dialysis solution are shown in Table 3.

[0069] Table 3

[0070]

[0071] As shown in Table 3, the reverse osmosis membrane filtration device 300 can separate dialysis fluid containing 253 mg / L ammonium sulfate into dialysis fluid with ammonia nitrogen less than 1.0 mg / L and total nitrogen less than 1.5 mg / L, and a concentrated solution with an ammonium sulfate concentration of 2526 mg / L. Except for other pollutant indicators, the dialysis fluid fully meets the emission standards of Table 2 of the "Rare Earth Industry Pollutant Emission Standard" (GB26451-2011) and the Class IV water quality standards of Table 1 of the "Surface Water Environmental Quality Standard" (GB3838-2011). The yield of the dialysis fluid is 90%. The concentrated solution containing 2526 mg / L ammonium sulfate is pumped back to the nanofiltration separation device 200.

[0072] Example 2

[0073] See Figure 1 and Figure 2 The rare earth wastewater containing 1200 mg / L ammonium sulfate, as provided in this embodiment, undergoes ammonium sulfate recovery and wastewater treatment. The system includes a filtration device 100, a spiral wound nanofiltration membrane filtration and separation device 200, and a disc tube reverse osmosis filtration and separation concentration device 300. The filter is a multi-media filter. The outlet of the second dialysis fluid storage tank 360 is connected to the inlet of a metering tank, and the fluid is discharged into a natural water body after being metered by the metering tank.

[0074] In this embodiment, the influent indicators and effluent compliance indicators of the rare earth high ammonia wastewater to be treated are shown in Table 4.

[0075] Table 4

[0076] Serial Number project Influent water parameters (mg / L) Effluent effluent standards (mg / L) Removal rate (%) 1 COD 37 20 45.95 2 BOD 11 6 45.45 3 SS 70 5 92.86 4 Total nitrogen (as N) 1015 1.5 99.85 5 Ammonia nitrogen (as N) 1100 1.0 99.91 6 Total phosphorus (as P) 1.7 0.1 94.12 7 Color intensity (dilution factor) 10 2 80 8 pH 6.5 6～9 -

[0077] The method for recovering ammonium sulfate from rare earth wastewater and treating the wastewater in this embodiment includes three steps: filtration, nanofiltration membrane filtration, and disc tube reverse osmosis filtration. Specifically:

[0078] The rare earth wastewater to be treated is collected in the rare earth wastewater equalization tank 110. The rare earth wastewater is pumped into the filter 130 by the first high-pressure pump 120 to obtain filtrate, which is then stored in the filtrate storage tank 160. Solid particles are removed and the solids are collected in the filter residue collection tank.

[0079] The filtrate obtained from filtration and stored in filtrate storage tank 160 is pumped by a second high-pressure pump 210 into nanofiltration membrane module 220 of nanofiltration membrane filtration (separation, concentration, and recovery of ammonium sulfate) device 200. The inlet water pressure of the nanofiltration membrane module is adjusted to 15 bar at the inlet and 13.5 bar at the outlet. After filtration by nanofiltration membrane module 220, nanofiltration concentrate and nanofiltration dialysis solution are obtained. The effluent from nanofiltration concentrate is stored in nanofiltration concentrate storage tank 270, and the effluent from nanofiltration dialysis solution is stored in nanofiltration dialysis solution storage tank 260. The water production rate of the concentrate was measured to be 9%, and the ammonia nitrogen concentration of ammonium sulfate increased from 1100 mg / L to 9390 mg / L, which is equivalent to an ammonium sulfate concentration of 3.612%. The water production rate of the nanofiltration dialysis solution was 91%, and its ammonium sulfate concentration was measured to be 280 mg / L. The nanofiltration concentrate with an ammonium sulfate concentration of 3.612% is the recovered ammonium sulfate solution, which is then used as the leaching solution in rare earth mining. Nanofiltration dialysis solution containing 280 mg / L of ammonium sulfate enters the reverse osmosis membrane filtration separation unit 300.

[0080] The nanofiltration dialysis solution, stored in the first dialysis solution storage tank 260, is pumped into the reverse osmosis membrane module 320 of the reverse osmosis membrane filtration and separation device 300 via a third high-pressure pump. The inlet water pressure of the reverse osmosis membrane module is adjusted to 65 bar at the inlet and 63.5 bar at the outlet. The reverse osmosis solution and reverse osmosis dialysis solution are separated by filtration through the reverse osmosis membrane module. The effluent from the reverse osmosis membrane concentrate is stored in the nanofiltration membrane concentrate storage tank 270, and the effluent from the reverse osmosis membrane dialysis solution is stored in the reverse osmosis dialysis solution storage pool 360. The permeate rate of the reverse osmosis membrane concentrate is measured to be 8%, and the ammonia nitrogen concentration of ammonium sulfate increases from 280 mg / L to 3480 mg / L. The permeate rate of the nanofiltration dialysis solution is 92%, and its ammonium sulfate concentration is measured to be 4.8 mg / L. The main pollutant indicators are shown in Table 5.

[0081] Table 5

[0082]

[0083] As shown in Table 5, after treatment by the membrane method for recovering ammonium sulfate from rare earth wastewater, a 10% concentrate containing 3.019% ammonium sulfate can be recovered. After catalytic electrolytic denitrification, the effluent ammonia nitrogen is less than 1.3 mg / L, total nitrogen is less than 1.5 mg / L, and all other major pollutants fully meet the emission standards of Table 2 of the "Rare Earth Industry Pollutant Discharge Standard" (GB26451-2011) and the Class IV water quality standards of Table 1 of the "Surface Water Environmental Quality Standard" (GB3838-2011). The reverse osmosis concentrate with an ammonium sulfate concentration of 3480 mg / L is pumped back into the nanofiltration separation device 200.

[0084] Example 3

[0085] See Figure 3 and Figure 4 The membrane-based treatment system for recovering ammonium sulfate and rare earth wastewater provided in this embodiment includes a microfiltration device 100, a nanofiltration membrane filtration separation device 200, and a reverse osmosis membrane filtration separation device 300.

[0086] The microfiltration device 100 employs a microfiltration membrane module 160', which is used to filter out solid particulate impurities from rare earth wastewater and prevent subsequent membrane clogging.

[0087] The nanofiltration membrane filtration (ammonium sulfate solution separation and recovery) device 200 employs a spiral wound nanofiltration membrane module 220 with a magnesium sulfate rejection rate ≥98%. A second high-pressure pump 210 is used to transport the filtrate obtained from the rare earth wastewater filtration to the spiral wound nanofiltration membrane module 220. The spiral wound nanofiltration membrane module 220 is used to filter and separate the rare earth wastewater into a concentrated solution with a higher ammonium sulfate concentration and a dialysate containing a small amount of ammonium sulfate. The membrane concentrate (ammonium sulfate concentrate) storage tank 270 is used to store the high-concentration ammonium sulfate concentrate separated by the spiral wound nanofiltration membrane module 220, and the first dialysate storage tank 260 is used to store the dialysate containing a small amount of ammonium sulfate separated by the spiral wound nanofiltration membrane module 220.

[0088] The reverse osmosis filtration device 300 employs a spiral wound reverse osmosis membrane module 320 with a sodium chloride rejection rate greater than 98%. A third high-pressure pump 310 is used to transport the dialysis filtrate obtained from nanofiltration of rare earth wastewater into the spiral wound reverse osmosis membrane module 320. The spiral wound reverse osmosis membrane module 320 is used to filter and separate the dialysis filtrate containing a small amount of ammonium sulfate from the nanofiltration of rare earth wastewater into a reverse osmosis concentrate with a higher ammonium sulfate content and a dialysis filtrate with a lower ammonium sulfate concentration. The outlet of the second dialysis filtrate storage tank 360 is connected to the inlet of the drainage metering tank, and the filtrate is discharged into a natural water body after metering.

[0089] In this embodiment, the influent indicators and effluent compliance indicators of the rare earth high ammonia wastewater to be treated are shown in Table 6.

[0090] Table 6

[0091] Serial Number project Influent water parameters (mg / L) Effluent effluent standards (mg / L) Removal rate (%) 1 COD 40 20 50.00 2 BOD 15 6 60.00 3 SS 150 5 96.67 4 Total nitrogen (as N) 1705 1.5 99.91 5 Ammonia nitrogen (as N) 1650 1.0 99.94 6 Total phosphorus (as P) 1.5 0.1 93.33 7 Color intensity (dilution factor) 10 2 80 8 pH 6.5 6～9 -

[0092] The membrane method used in this embodiment for recovering ammonium sulfate and treating rare earth wastewater includes three steps in sequence: microfiltration, nanofiltration, and reverse osmosis. Specifically:

[0093] The rare earth wastewater to be treated is collected in the rare earth wastewater equalization tank 110'. The wastewater treated by the security filter 130' is pumped into the microfiltration membrane module 160' by the first high-pressure pump 150'. The filtrate obtained by the microfiltration membrane module 160' is stored in the filtrate storage tank 190'.

[0094] The filtrate obtained from filtration and stored in the filtrate storage tank 190' is pumped into the spiral-wound nanofiltration membrane module 220 of the spiral-wound nanofiltration membrane separation device 200 by the second high-pressure pump 210. The inlet water pressure of the membrane module is adjusted to 15 bar at the inlet and 13.5 bar at the outlet. After filtration by the nanofiltration membrane module 220, nanofiltration concentrate and nanofiltration dialysate are obtained. The effluent from the nanofiltration membrane concentrate is stored in the nanofiltration concentrate storage tank 230, and the effluent from the nanofiltration membrane dialysate is stored in the nanofiltration dialysate storage tank 260. The water production rate of the nanofiltration membrane concentrate was measured to be 12%, and the ammonia nitrogen concentration of ammonium sulfate increased from 1650 mg / L to 10960 mg / L, which is equivalent to an ammonium sulfate concentration of 4.215%. The water production rate of the nanofiltration dialysate was 88%, and its ammonium sulfate concentration was measured to be 380.5 mg / L.

[0095] The nanofiltration dialysis solution obtained from nanofiltration and stored in the dialysis solution storage tank 260 is pumped into the reverse osmosis membrane module 320 of the spiral wound reverse osmosis membrane filtration and separation device 300 by a high-pressure pump 310. The inlet water pressure of the reverse osmosis membrane module is adjusted to 16 bar at the inlet and 14.5 bar at the outlet. After filtration and separation by the reverse osmosis membrane module 320, reverse osmosis concentrate and reverse osmosis dialysis solution are obtained. The effluent from the reverse osmosis membrane concentrate is stored in the nanofiltration membrane concentrate storage tank 270, and the effluent from the reverse osmosis membrane dialysis solution is stored in the reverse osmosis dialysis solution storage tank 360. The permeate rate of the reverse osmosis membrane concentrate is measured to be 9.5%, and the ammonia nitrogen concentration of ammonium sulfate increases from 380.5 mg / L to 3950 mg / L, which is equivalent to an ammonium sulfate concentration of 3.019%. The reverse osmosis membrane concentrate is pumped back to the nanofiltration filtration device. The permeate rate of the reverse osmosis dialysis solution is 90.5%, and its ammonium sulfate concentration is measured to be 5.8 mg / L. The main pollutant indicators are shown in Table 7.

[0096] Table 7

[0097]

[0098] In summary, after treatment with the membrane-based ammonium sulfate recovery system and method for rare earth wastewater, 12% of a 4.215% ammonium sulfate concentrate can be recovered. After reverse osmosis treatment, the effluent (see Table 7) shows that the main pollutant indicators (ammonia nitrogen and total nitrogen) are less than 1.0 mg / L and less than 1.5 mg / L, respectively. Except for other main pollutant indicators, the effluent fully meets the emission standards of Table 2 of the "Rare Earth Industry Pollutant Emission Standard" (GB26451-2011) and the Class IV water quality standard of the "Surface Water Environmental Quality Standard" (GB3838-2011).

[0099] Example 4

[0100] See Figure 3 and Figure 4 The membrane-based treatment system for recovering ammonium sulfate and rare earth wastewater provided in this embodiment includes an ultrafiltration filtration device 100, a spiral wound nanofiltration membrane filtration separation device 200, and a disc tube reverse osmosis membrane filtration separation device 300.

[0101] The ultrafiltration device 100 uses an ultrafiltration membrane module 160'; the spiral wound nanofiltration membrane filtration (for separating and recovering ammonium sulfate solution) uses a spiral wound nanofiltration membrane module 220 with a magnesium sulfate rejection rate ≥98%; the disc tube reverse osmosis filtration device 300 uses a disc tube reverse osmosis membrane module 320 with a sodium chloride rejection rate greater than 98%.

[0102] In this embodiment, the influent indicators and effluent compliance indicators of the rare earth high ammonia wastewater to be treated are shown in Table 8.

[0103] Table 8

[0104] Serial Number project Influent water parameters (mg / L) Effluent effluent standards (mg / L) Removal rate (%) 1 COD 35 20 42.86 2 BOD 15 6 60.00 3 SS 150 5 96.67 4 Total nitrogen (as N) 705 1.5 93.80 5 Ammonia nitrogen (as N) 690 1.0 99.86 6 Total phosphorus (as P) 1.5 0.1 93.33 7 Color intensity (dilution factor) 10 2 80 8 pH 6.5 6～9 -

[0105] The membrane method used in this embodiment for recovering ammonium sulfate and treating rare earth wastewater includes three steps in sequence: microfiltration, nanofiltration, and reverse osmosis. Specifically:

[0106] The rare earth wastewater to be treated is collected in the rare earth wastewater equalization tank 110'. The wastewater treated by the security filter 130' is pumped into the ultrafiltration membrane module 160' by the first high-pressure pump 150'. The filtrate obtained by the ultrafiltration membrane module 160' is stored in the filtrate storage tank 190'.

[0107] The filtrate obtained from filtration and stored in filtrate storage tank 190' is pumped into spiral-wound nanofiltration membrane module 220 in spiral-wound nanofiltration separation device 200 by high-pressure pump 210. The inlet water pressure of the membrane module is adjusted to 15 bar at the inlet and 13.5 bar at the outlet. After filtration by nanofiltration membrane module 220, nanofiltration concentrate and nanofiltration dialysate are obtained. The effluent from nanofiltration concentrate is stored in nanofiltration concentrate storage tank 270, and the effluent from nanofiltration dialysate is stored in nanofiltration dialysate storage tank 260. The water production rate of nanofiltration concentrate was measured to be 5.6%, and the ammonia nitrogen concentration of ammonium sulfate increased from 690 mg / L to 8960 mg / L, which is equivalent to an ammonium sulfate concentration of 3.446%. The water production rate of nanofiltration dialysate was 94.4%, and its ammonium sulfate concentration was measured to be 199.4 mg / L.

[0108] The nanofiltration solution obtained and stored in the first dialysis solution storage tank 260 is pumped into the reverse osmosis membrane module 320 of the disc tube reverse osmosis membrane filtration and separation device 300 by a high-pressure pump 310. The inlet water pressure of the reverse osmosis membrane module is adjusted to 36 bar at the inlet and 34.5 bar at the outlet. After filtration and separation by the reverse osmosis membrane module 320, reverse osmosis concentrate and reverse osmosis dialysis solution are obtained. The effluent from the reverse osmosis membrane concentrate is stored in the nanofiltration membrane concentrate storage tank 270, and the effluent from the reverse osmosis membrane dialysis solution is stored in the reverse osmosis dialysis solution storage tank 360. The permeate rate of the reverse osmosis membrane concentrate is measured to be 6.0%, and the ammonia nitrogen concentration of ammonium sulfate increases from 199.4 mg / L to 3310 mg / L, which is equivalent to an ammonium sulfate concentration of 3.019%. The reverse osmosis membrane concentrate is pumped back to the nanofiltration filtration device 200. The permeate rate of the reverse osmosis dialysis solution is 94.0%, and its ammonium sulfate concentration is measured to be 0.85 mg / L. The main pollutant indicators are shown in Table 9.

[0109] Table 9

[0110]

[0111] In summary, after treatment with the membrane method for recovering ammonium sulfate and rare earth wastewater, 5.6% of a concentrated solution containing 3.446% ammonium sulfate can be recovered. After reverse osmosis treatment, the effluent (see Table 9) shows that the main pollutant indicators (ammonia nitrogen and total nitrogen) are less than 1.0 mg / L and less than 1.5 mg / L, respectively. Except for other main pollutant indicators, the effluent fully meets the emission standards of Table 2 of the "Rare Earth Industry Pollutant Discharge Standard" (GB26451-2011) and the Class IV water quality standards of Table 1 of the "Surface Water Environmental Quality Standard" (GB3838-2011).

[0112] Example 5

[0113] See Figure 3 and Figure 4This embodiment provides a membrane-based treatment system for recovering ammonium sulfate and rare earth wastewater from rare earth wastewater, comprising an ultrafiltration filtration device 100, a disc tube nanofiltration membrane filtration separation device 200, and a spiral wound reverse osmosis membrane filtration separation device 300. The ultrafiltration filtration device 100 employs an ultrafiltration membrane module 160'.

[0114] In this embodiment, the influent indicators and effluent compliance indicators of the rare earth high ammonia wastewater to be treated are shown in Table 10.

[0115] Table 10

[0116] Serial Number project Influent water parameters (mg / L) Effluent effluent standards (mg / L) Removal rate (%) 1 COD 40 20 50.00 2 BOD 15 6 60.00 3 SS 90 5 94.44 4 Total nitrogen (as N) 1810 1.5 99.92 5 Ammonia nitrogen (as N) 1790 1.0 99.94 6 Total phosphorus (as P) 1.5 0.1 93.33 7 Color intensity (dilution factor) 10 2 80 8 pH 6.5 6～9 -

[0117] The membrane method used in this embodiment for recovering ammonium sulfate and treating rare earth wastewater includes three steps in sequence: microfiltration, nanofiltration, and reverse osmosis. Specifically:

[0118] The rare earth wastewater to be treated is collected in the rare earth wastewater equalization tank 110'. The wastewater treated by the security filter 130' is pumped into the ultrafiltration membrane module 160' by the first high-pressure pump 150'. The filtrate obtained by the ultrafiltration membrane module 160' is stored in the filtrate storage tank 190'.

[0119] The filtrate obtained from filtration and stored in the filtrate storage tank 190' is pumped into the disc tube nanofiltration membrane module 220 of the disc tube nanofiltration membrane separation device 200 by the high-pressure pump 210. The inlet water pressure of the membrane module is adjusted to 35 bar at the inlet and 33.5 bar at the outlet. After filtration by the disc tube nanofiltration membrane module 220, nanofiltration concentrate and nanofiltration dialysate are obtained. The effluent from the nanofiltration membrane concentrate is stored in the nanofiltration concentrate storage tank 270, and the effluent from the nanofiltration membrane dialysate is stored in the nanofiltration dialysate storage pool 260. The water production rate of the nanofiltration membrane concentrate was measured to be 15.0%, and the ammonia nitrogen concentration of ammonium sulfate increased from 1790 mg / L to 11350 mg / L, which is equivalent to an ammonium sulfate concentration of 4.365%. The water production rate of the nanofiltration dialysate was 84.7%, and its ammonium sulfate concentration was measured to be 102.94 mg / L.

[0120] The nanofiltration dialysis solution obtained from nanofiltration and stored in the first dialysis solution storage tank 260 is pumped into the reverse osmosis membrane module 320 of the spiral wound reverse osmosis membrane filtration and separation device 300 by a high-pressure pump 310. The inlet water pressure of the reverse osmosis membrane module is adjusted to 15 bar at the inlet and 14.0 bar at the outlet. After filtration and separation by the reverse osmosis membrane module 320, reverse osmosis concentrate and reverse osmosis dialysis solution are obtained. The effluent from the reverse osmosis membrane concentrate is stored in the concentrate storage tank 270, and the effluent from the reverse osmosis membrane dialysis solution is stored in the reverse osmosis dialysis solution storage tank 360. The permeate rate of the reverse osmosis membrane concentrate is measured to be 5.0%, and the ammonia nitrogen concentration of ammonium sulfate increases from 102.94 mg / L to 2050 mg / L. The reverse osmosis membrane concentrate is pumped back to the nanofiltration filtration device 200. The permeate rate of the reverse osmosis dialysis solution is 95.0%, and its ammonium sulfate concentration is measured to be 1.0 mg / L. The main pollutant indicators are shown in Table 11.

[0121] Table 11

[0122]

[0123] In summary, after treatment with the membrane method for recovering ammonium sulfate and rare earth wastewater, 15.0% of a concentrated solution containing 4.365% ammonium sulfate can be recovered. After reverse osmosis treatment, the effluent (see Table 9) shows that the main pollutant indicators (reverse osmosis membrane dialysis solution) are less than 1.0 mg / L for ammonia nitrogen and less than 1.5 mg / L for total nitrogen. Except for other main pollutant indicators, it fully meets the emission standards of Table 2 of the "Rare Earth Industry Pollutant Discharge Standard" (GB26451-2011) and the Class IV water quality standards of Table 1 of the "Surface Water Environmental Quality Standard" (GB3838-2011).

[0124] The foregoing description illustrates and describes preferred embodiments of the present invention. As previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A membrane-based treatment system for recovering ammonium sulfate from rare earth wastewater, characterized in that, Includes filtration devices, nanofiltration membrane filtration devices, and reverse osmosis membrane filtration devices: The filtration device includes a rare earth wastewater regulating tank, a first high-pressure pump, a filter, a first eluent storage tank, a first backwash water tank, and a filtrate storage tank. The inlet of the first high-pressure pump is connected to the rare earth wastewater regulating tank, the outlet of the first high-pressure pump is connected to the inlet of the filter, the outlet of the filter is connected to the inlet of the filtrate storage tank, the backwash water outlet of the filter is connected to the first eluent storage tank, and the outlet of the first backwash water tank is connected to the filter. The nanofiltration membrane filtration separation device includes a second high-pressure pump, a nanofiltration membrane module, a nanofiltration eluent storage tank, a first chemical washing tank, a second backwash water tank, a first dialysis fluid storage tank, a nanofiltration membrane concentrate storage tank, and a sludge thickening tank. The inlet of the second high-pressure pump is connected to the filtrate storage tank, and the outlet of the second high-pressure pump is connected to the inlet of the nanofiltration membrane module. The dialysis fluid outlet of the nanofiltration membrane module is connected to the inlet of the first dialysis fluid storage tank, and the concentrate outlet of the nanofiltration membrane module is connected to the nanofiltration membrane concentrate storage tank. The outlet of the first dialysis fluid storage tank is connected to the reverse osmosis membrane filtration separation device, the eluent outlet of the nanofiltration membrane module is connected to the nanofiltration eluent storage tank, the supernatant outlet of the nanofiltration eluent storage tank is connected to a rare earth wastewater equalization tank, and the sludge outlet of the nanofiltration eluent storage tank is connected to the sludge thickening tank. The reverse osmosis membrane filtration separation device includes a third high-pressure pump, a reverse osmosis membrane module, a reverse osmosis eluent storage tank, a second chemical washing tank, a second backwash water tank, and a second dialysis fluid storage tank. The inlet of the third high-pressure pump is connected to the first dialysis fluid storage tank, the outlet of the third high-pressure pump is connected to the inlet of the reverse osmosis membrane module, the dialysis fluid outlet of the reverse osmosis membrane module is connected to the inlet of the second dialysis fluid storage tank, and the concentrate outlet of the reverse osmosis membrane module is connected to the nanofiltration membrane concentrate storage tank. The nanofiltration membrane module of the nanofiltration separation device is a nanofiltration membrane module that retains magnesium sulfate at a concentration greater than or equal to 98%. The membrane material of the nanofiltration membrane module is an organic membrane or a composite membrane. The working pressure is: inlet 15-55 bar, outlet 13.5-53 bar, and the pressure difference between the inlet and outlet is 1.5-2.0 bar. The reverse osmosis membrane module of the reverse osmosis membrane filtration separation device is a reverse osmosis filter membrane module with a sodium chloride rejection of greater than or equal to 98%. The membrane material of the reverse osmosis membrane module is an organic membrane or a composite membrane. The working pressure is 15-75 bar at the inlet and 13.5-73 bar at the outlet. The pressure difference between the inlet and outlet is 1-1.5 bar. The nanofiltration membrane filtration separation device is used to separate rare earth wastewater into a concentrated solution containing 2-6% ammonium sulfate and a dialysis solution with an ammonium sulfate concentration of less than 700 mg / L.

2. The membrane-based ammonium sulfate recovery system for rare earth wastewater according to claim 1, characterized in that, The filter is a mechanical filter or a membrane module.

3. The membrane-based ammonium sulfate recovery system for rare earth wastewater according to claim 2, characterized in that, The mechanical filter is one of the following: sand filter, activated sand filter, multi-media filter, V-type filter, fine filter, or fiber filter cartridge filter.

4. The membrane-based ammonium sulfate recovery system for rare earth wastewater according to claim 2, characterized in that, The membrane module of the filter is either a microfiltration or ultrafiltration membrane module.

5. The membrane-based ammonium sulfate recovery system for rare earth wastewater according to claim 4, characterized in that, The microfiltration or ultrafiltration membrane module is one of the following: tubular membrane module, spiral wound membrane module, hollow fiber membrane module, or flat sheet membrane module.

6. The membrane-based ammonium sulfate recovery system for rare earth wastewater according to claim 4, characterized in that, The filtration device also includes a booster pump and a security filter. The inlet of the booster pump is connected to the rare earth wastewater regulating tank, the outlet of the booster pump is connected to the inlet of the security filter, and the outlet of the security filter is connected to the microfiltration or ultrafiltration membrane assembly.

7. A membrane-based treatment system for recovering ammonium sulfate from rare earth wastewater according to any one of claims 1-6, characterized in that, The nanofiltration membrane module or reverse osmosis membrane module is one of a tubular membrane module, a spiral wound membrane module, a hollow fiber membrane module, a flat sheet membrane module, or a disc tube membrane module.

8. A method for membrane-based recovery of ammonium sulfate from rare earth wastewater, characterized in that, The treatment system for recovering ammonium sulfate from rare earth wastewater using a membrane method according to any one of claims 1-7 is used to process the wastewater according to the following steps: (1) Rare earth wastewater filtration: The rare earth wastewater to be treated is collected in the rare earth wastewater equalization tank, and then pumped into the filter to obtain filtrate and filter residue. The filtrate is stored in the filtrate storage tank. (2) Nanofiltration membrane filtration separation, concentration and recovery of ammonium sulfate solution: The filtrate obtained from the filtration in step (1) and stored in the filtrate storage tank is sent to the nanofiltration membrane filtration separation device by a high-pressure pump. The inlet pressure is 15-55 bar, the outlet pressure is 13.5-53 bar, and the pressure difference between the inlet and outlet is 1-1.5 bar. Rare earth wastewater is separated into a concentrated solution containing 2-6% ammonium sulfate and a dialysis solution with an ammonium sulfate concentration of less than 700 mg / L by nanofiltration. These solutions are stored separately in a nanofiltration membrane concentrated solution storage tank and a first dialysis solution storage tank. The yield of the concentrated solution containing 2-6% ammonium sulfate is 15-20%, and the yield of the dialysis solution with an ammonium sulfate concentration of less than 700 mg / L is 80-85%. The concentrated solution containing 2-6% ammonium sulfate is the recovered ammonium sulfate solution and can be used as a leaching solution for rare earth mining. (3) Reverse osmosis membrane filtration: The nanofiltration solution obtained in step (2) and stored in the first dialysis solution storage tank is pumped into the reverse osmosis membrane filtration separation device using a third high-pressure pump. The working inlet pressure is 15-75 bar, the outlet pressure is 13.5-73 bar, and the pressure difference is 1-1.5 bar. The reverse osmosis membrane filtration separation device separates the nanofiltration solution of rare earth wastewater into a concentrated solution containing ammonium sulfate with a concentration of 3500-4500 mg / L and a solution containing ammonia nitrogen with a concentration of less than 25 mg / L. The solutions are stored separately in a nanofiltration membrane concentrate tank and a second dialysis solution tank. The yield of the concentrate containing ammonium sulfate concentration of 3500-4500 mg / L is 5-15%. The yield of the dialysis solution containing ammonia nitrogen concentration of less than 25 mg / L is 85-95%. The concentrate containing ammonium sulfate concentration of 3500-4500 mg / L is pumped back to the nanofiltration membrane filtration separation device for further nanofiltration. The reverse osmosis dialysis solution containing ammonia nitrogen concentration of less than 25 mg / L is discharged into natural water bodies after metering.

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